Physics Engine (#4)

* Add matter-js as a dependency

* Add body component

* Fix renderable node doc

* Add the physics node type

* Correct typo in physics enabled node types

* Update docs on render system

* Add physics system

* Update changelog

* Add physics engine to main app

* Tweak the gravity of the world

* Add body to sumo factory

* Add angle component

* Add angle to entity

* Add angle to the nodes

* Pass angle between systems

* Set default angle to 0

* Split systems and nodes

* Fix indentaion in physics world control

* Add third sumo entity

* Adjust values for constriants and physics

* Correct docs in new nodes

* Update built-in docs

1 files changed, 98 insertions, 0 deletions

diff --git a/lib/systems/physics_world_control.js b/lib/systems/physics_world_control.js
new file mode 100644
index 0000000..daa39c1
--- /dev/null
+++ b/lib/systems/physics_world_control.js
@@ -0,0 +1,98 @@
+import { System } from '@serpentity/serpentity';
+import { Engine, World } from 'matter-js';
+
+import PhysicalNode from '../nodes/physical';
+
+const internals = {
+  kNoEngine: 'No matter js physics engine found. Make sure you set the `engine` key in the config object when initializing.'
+};
+
+/**
+ * Adds and removes objects to the physics world and calls update
+ *
+ * @extends {external:Serpentity.System}
+ * @class PhysicsWorldControlSystem
+ * @param {object} config a configuration object to extend.
+ */
+export default class PhysicsWorldControlSystem extends System {
+
+  constructor(config = {}) {
+
+    super();
+
+    /**
+     * The node collection of physics entities
+     *
+     * @property {external:Serpentity.NodeCollection} physicalEntities
+     * @instance
+     * @memberof PhysicsWorldControlSystem
+     */
+    this.physicalEntities = null;
+
+    /**
+     * The matter-js engine we will use to process physics
+     *
+     * @property {external:MatterJs.Engine} engine
+     * @instance
+     * @memberof PhysicsWorldControlSystem
+     */
+    this.engine = config.engine;
+
+    if (!this.engine) {
+      throw new Error(internals.kNoEngine);
+    }
+  }
+
+  /**
+   * Initializes system when added. Requests physics nodes and
+   * attaches to event listeners to add / remove them to pixi stage
+   *
+   * @function added
+   * @memberof PhysicsWorldControlSystem
+   * @instance
+   * @param {external:Serpentity.Engine} engine the serpentity engine to
+   * which we are getting added
+   */
+  added(engine) {
+
+    this.physicalEntities = engine.getNodes(PhysicalNode);
+    this.physicalEntities.on('nodeAdded', (event) => {
+
+      World.add(this.engine.world, [event.node.body.body]);
+    });
+    this.physicalEntities.on('nodeRemoved', (event) => {
+
+      World.remove(this.engine.world, [event.node.body.body]);
+    });
+  }
+
+  /**
+   * Clears system resources when removed.
+   *
+   * @function removed
+   * @instance
+   * @memberof PhysicsWorldControlSystem
+   */
+  removed() {
+
+    this.physicalEntities.removeAllListeners('nodeAdded');
+    this.physicalEntities.removeAllListeners('nodeRemoved');
+    this.physicalEntities = null;
+  }
+
+  /**
+   * Runs on every update of the loop. Updates the physics
+   *
+   * @function update
+   * @instance
+   * @param {Number} currentFrameDuration the duration of the current
+   * frame
+   * @memberof PhysicsWorldControlSystem
+   */
+  update(currentFrameDuration) {
+
+    Engine.run(this.engine);
+  }
+};
+
+